1. Field of the Invention
The present invention relates to a stereoscopic display. Such a display may be used, for example, as a reflective display and in hand-held devices such as small dedicated game computers.
2. Description of the Related Art
A known type of stereoscopic display is disclosed in U.S. Pat. No. 5,537,144. The display is of the spatially multiplexed micropolariser type. Two complementary checkerboard masks are used to select complementary checkerboard patterns of picture elements (pixels) of the two two dimensional (2D) images to be displayed. The selected pixels from the two images are interlaced to form a composite spatially multiplexed image. A micropolariser is then disposed over the composite image so that light from the left view pixels is polarised with a first polarisation and light from the right view pixels is polarised with a second polarisation orthogonal to the first polarisation. An observer wears viewing spectacles comprising orthogonally oriented polarisers so that the left eye can see only the left view pixels whereas the right eye can see only the right view pixels.
Although U.S. Pat. No. 6,5537,144 discloses in detail the checkerboard patterns with right and left view pixels alternating with each other horizontally and vertically in the composite image, there is a suggestion that other patterns are possible. In particular, there is brief reference to a one dimensional array of polariser stripes but no other information is given concerning such an arrangement. Also, the use of a patterned retarder with a uniform polariser to form the micropolariser ie described. In such an arrangement, light from the composite image is first polarised by the uniform polariser. A suitable pattern of retarders is then formed so as to rotate the polarisation of light from either the left or the right pixels so as to maintain the orthogonal polarization.
U.S. Pat. No. 5,537,144 is not concerned with the effects of parallax resulting from the spacing between the micropolariser and the composite image. Similarly, there is no mention or consideration of viewing angle performance.
A known type of stereoscopic display based on the teachings of U.S. Pat. No. 5,537,144 is known as xe2x80x9cCyberBookxe2x80x9d and is available from VREX Inc., a division of Reveco Inc. FIG. 1 of the accompanying drawings illustrates this type of display, which comprises a spatial light modulator (SLM) 1 in the form of a liquid crystal device (LCD). The SLM 1 comprises front and rear transparent substrates 2 and 3 defining a cell containing a liquid crystal layer 4. The display also comprises a back light (not shown) for directing light through the SLM 1 towards a viewing region 5.
The SLM 1 comprises a rectangular array of pixels, one of which is indicated diagrammatically at 6. The front substrate carries on its external surface a linear polariser 7 and an array of horizontal retarder stripes such as 8. The polariser 7 and the array of retarder stripes 8 form a micropolariser. In particular, light from the SLM 1 passing through the polariser 7 emerges with a first linear polarisation. The vertical width of the stripes 8 may be slightly less than the vertical pitch of the pixels 6 so as to ensure that an observer located in the viewing region 5 can see every row of pixels 6 of the SLM 1 through the correct retarder stripe 8 or a gap between adjacent retarder stripes. This is generally referred to as xe2x80x9cviewpoint correctionxe2x80x9d.
Light passing from rows of pixels 6 aligned with gaps between the stripes 8 of the retarder propagated to the viewing region 5 with the linear polarization determined by the polariser 7. Light from the rows of pixel 6 passing through the aligned stripes 8 of the retarder have their linear polarisation rotated through 90xc2x0. An observer indicated diagrammatically at 9 wears viewing spectacles with polarisers 10 and 11 which are oriented so that, for example, the polariser 10 passes light whose polarisation has been rotated by the retarder stripes 8 and attenuates light received directly from the polariser 7 whereas the polariser 11 passes light received directly from the polariser 7 but attenuates light received from the retarder stripes 8. If the polarisers 10 and 11 are worn over the left and right eyes respectively, of the observer 9, and if the rows of pixels aligned with the retarder stripes 8 display left view image data whereas the rows of pixels aligned with the gaps between the retarder stripes 8 display right view image data, the observer 9 perceives a stereoscopic three dimensional (3D) image.
Because the retarder stripes 8 extend horizontally, the observer 9 has considerable freedom of movement in a horizontal direction relative to the display and no undesirable visual artefacts will occur because of parallax between the stripes and the pixel apertures which are separated by the thickness of the substrate 2 and the polariser 7. However, the vertical freedom of movement is far more limited. In a typical example of a display of this type, the front substrate 2 is approximately 1.1 millimeters thick whereas the vertical pitch of the pixels 6 is typically about 300 micrometers. Correct performance of the display relies on the observer seeing the rows of pixels 6 through the respectively aligned retarder stripes 8 or gaps therebetween. Vertical movement of the observer 9 relative to the display out of the intended viewing region 5 immediately results in undesirable visual artefacts. In particular, as the line-of-sight alignment of the pixel rows and the retarder stripes 8 or gaps therebetween becomes lost, dimming artefacts and then crosstalk between the left and right images become visible. Further vertical movement results in the pixel rows displaying the left and right view image data being seen by the right and left eyes, respectively, of the observer 9 i.e. pseudoscopic viewing. Such visual artefacts are most undesirable so that the vertical freedom of movement of the observer 9 for correctly viewing the display is severely limited.
Thus, displays of the type shown in FIG. 1 are of practical use only in applications where the limited vertical viewing freedom is not a problem, for example in desktop displays. Displays of this type are not suitable for reflective displays, where the display is generally tilted according to the prevailing lighting conditions so as to give the best display brightness, and for hand-held displays, such as dedicated games computers which are tilted during the playing process. This is illustrated in FIG. 2 of the accompanying drawings, where an observer 9 tilts a display 1 in a direction indicated by a double-headed arrow 13 so as to obtain a best view of the display. A reflective display is typically illuminated by an overhead source 14 such as the sun, a lamp or a fluorescent tube. Such a bright small source tends to result in specular reflection an shown at 15 and the observer tilts the display so as to maximise display brightness while avoiding the specular reflection as shown at 15. The observer 9 may also obtain a best view on the other side of the specular reflection.
FIG. 3 of the accompanying drawings illustrates another known type of stereoscopic display, for example as disclosed in Japanese patent publication no. 9-304740. The display is of the transmissive type and is similar to that shown in FIG. 1 except that a lenticular screen 12 whose cylindrically converging lenticules are oriented horizontally is disposed in front of the retarder array 8. In FIG. 3, the difference between the vertical pitch of the pixels 6 and the vertical pitch of the retarder stripe 8 is exaggerated to illustrate the viewpoint correction. The vertical pitch of the lenticules of the screen 12 is substantially equal to that of the retarder array 8 but, depending on the spacing between the lenticules 12 and the retarder stripes 8, is slightly less so as to match the viewpoint correction.
The provision of the lenticular screen 12 substantially increases the vertical size of the viewing zone 5 and thus increases the vertical freedom of movement of an observer. However, the lenticular screen 12 must be manufactured to high tolerance for a high resolution display and must be accurately aligned with the retarder stripes 8 end the rows of pixels 6 in order to function correctly and avoid undesirable visual artefacts.
Whereas the display shown in FIG. 1 may be used to display 2D images at full resolution and with large viewing freedom merely by the observer 9 removing the viewing spectacles, the display of FIG. 3 when viewed without polarising glasses is less effective for 2D viewing. The lenticular screen 12 converts the spatially varying opaque addressing electrodes, pixel and black mask pattern of the SLM 1 to an angular pattern such that black regions between the horizontal rows of pixels 6 are converted into substantial intensity artefacts in the 2D viewing mode. This substantially limits the artefact free vertical freedom of movement of the observer in the 2D mode. This is illustrated in FIG. 4 of the accompanying drawings, which illustrates black regions which are disposed between images of pixels and which represent images of black regions of the SLM 1 such as electrode lines covered by the black mask.
Although the display of FIG. 3 in 3D mode produces a larger orthoscopic viewing region in the vertical direction than that shown in FIG. 1, the pseudoscopic regions are similarly enlarged. Thus, there remains insufficient viewing freedom to operate a hand-held reflective display, which must retain extremely wide vertical viewing freedom in order to operate with the typical ambient overhead illumination.
JP 9-304740 also discloses an arrangement in which the retarder stripes and the lenticular screen are oriented vertically. The retarder stripe width is substantially equal to the pixel pitch. Although this arrangement improves the vertical viewing freedom of the display, the disadvantages associated with this type of lenticular screen remain.
GB 2 321 815 relates to an autostereoscopic display with a viewer position indicator to assist a viewer in positioning himself within the orthoscopic viewing regions so as to avoid the pseudoscopic regions. The display makes use of a spatial light modulator and a parallax optic for generating the parallax for 3D viewing and also for making the positioning indication visible in the appropriate viewing regions. In one set of embodiments, the parallax optic is a parallax barrier and details are given of a specific arrangement which makes use of a stripe-patterned retarder for varying the polarisation of light from the SLM with another polariser for analysing the output light to make the barrier structure visible. Thus, the retarder has relatively narrow slit regions and relatively wide barrier regions.
U.S. Pat. No. 5,317,393 discloses a stereoscopic display for use with crossed polarising glasses worn by an observer. An image display device has alternating columns for displaying left and right image strips with each pixel column lying behind a polariser. Adjacent polarisers have their polarizing directions arranged orthogonally. The pitch of the individual polariser strips is equal to the pitch of the pixels.
DE 3 203 339 discloses a stereoscopic display in which a vertically striped polariser is used in front of a television screen.
According to the invention, there is provided a stereoscopic display comprising a spatial light modulator having an array of picture elements and a retarder array having horizontally alternating first and second vertically extending stripes, the first and second stripes being arranged to supply light from the modulator with first and second polarisations, respectively, which are different from each other, characterized in that each of the first and second stripes has a width which is greater than the horizontal pitch of the picture elements.
The width of each of the first and second stripes may be substantially equal to twice the horizontal pitch of the picture elements. The picture elements may be arranged as groups of four in horizontally and vertically adjacent pairs and the picture elements of each group may comprise red, green, green or white, and blue picture elements.
The width of each of the first and second stripes may be substantially equal to three times the horizontal pitch of the picture elements. The picture elements may be arranged as horizontally adjacent triplets of red, green and blue picture elements, each triplet being aligned with a respective first or second stripe. The green picture element may be disposed between the red and blue picture elements of each triplet. Each of the red and blue picture elements may be narrower than the green picture element of each triplet.
The display may comprise a lenticular screen, each of whose lenticules is cylindrically converging and extends vertically, the horizontal pitch of the lenticules being substantially equal to the horizontal pitch of the picture elements. The lenticular screen may have a non-flat surface adjacent the modulator or the retarder.
The modulator may be arranged to provide controllable attenuation of light. The modulator may comprise a liquid crystal device.
The modulator may be of reflective type.
The second polarisation may be substantially orthogonal to the first polarisation.
It is also possible for the modulator to be a light-emitting modulator, such as an electroluminescent or field emission display.
The modulator may be arranged to supply linearly polarised light to the retarder array with the light being polarised parallel or perpendicular to a reference direction.
The first stripes may be arranged to rotate polarisation by 90xc2x0 and the second stripes may be arranged not to change polarization. The first stripes may comprise half wave retarders. The halt wave retarders may have optic axes oriented at substantially 45xc2x0 to the reference direction.
The first stripes may comprise first and second half wave retarders having optic axes oriented at substantially 22.5xc2x0 and substantially 67.5xc2x0, respectively, to the reference direction.
The first and second stripes may comprise half wave retarders whose optic axes are oriented at substantially +22.5xc2x0 and substantially xe2x88x9222.5xc2x0, respectively, to the reference direction. The first and second stripes may comprise a further half wave retarder whose optic axis is oriented at substantially 67.5xc2x0 to the reference direction.
The first and second stripes may comprise half wave retarders whose optic axes are oriented at substantially +67.5xc2x0 and substantially xe2x88x9267.5xc2x0, respectively, to the reference direction and a further half wave retarder whose optic axle is substantially parallel to the reference direction.
The first and second stripes may comprise quarter wave retarders whose optic axes are oriented at substantially +45xc2x0 and substantially xe2x88x9245xc2x0, respectively, to the reference direction and a further quarter wave retarder whose optic axis is oriented at substantially 45xc2x0 to the reference direction.
The display may comprise viewing spectacles having first and second linear polarisers with mutually orthogonal polarising directions.
The first and second stripes may comprise quarter wave retarders whose optic axes are oriented at substantially +45xc2x0 and substantially xe2x88x9245xc2x0, respectively, to the reference direction. The display may comprise viewing spectacles having first and second quarter wave retarders whose optic axes are oriented, in use, at substantially +45xc2x0 and substantially xe2x88x9245xc2x0, respectively, to the reference direction and first and second linear polarisers with substantially parallel polarising direction.
The display may comprise viewing spectacles having first and second half wave retarders whose optic axes are oriented, in use, at substantially +67.5xc2x0 and substantially xe2x88x9267.5xc2x0, respectively, to the reference direction and first and second linear polarisers with substantially parallel polarising directions. The first and second stripes may comprise a quarter wave retarder whose optic axis is oriented at substantially 90xc2x0 to the reference direction. The spectacles may comprise a quarter wave retarder whose optic axis is oriented, in use, substantially parallel to the reference direction.
It is thus possible to provide a display which is easier to manufacture than the known types of displays, for example as shown in FIGS. 1 and 2 of the accompanying drawings. For example, the pitch of the retarder array compared to the pixel pitch is substantially longer than in the known displays and is therefore easier to fabricate, particularly as display resolution increases. Substantially increased vertical viewing freedom is provided so that such displays may be used, for example, as reflective displays which can be oriented to make best use of ambient lighting without suffering from undesirable visual artefacts. A display of this type maintains full spatial resolution when used in a 2D mode, for which it is merely necessary for an observer not to view the display through a stereoscopic viewing aid such as viewing spectacles.
Although the horizontal viewing freedom is more limited, this is not a disadvantage in many applications and is more than offset by the increased vertical viewing freedom. The use of a lenticular screen allows the horizontal viewing freedom to be increased.
In the case of the RGB colour triplet embodiment, horizontal crosstalk initially occurs in the red and blue components whereas the green component, which in general contains most of the luminance information, is substantially less affected. Thus, undesirable visual effects of crosstalk are substantially reduced. Further, this arrangement may be more convenient in terms of electronic or software implementation or compatibility in that each triplet represents a single composite colour pixel so that image data are supplied in turn horizontally for the composite colour pixels instead of interweaving the individual colour component pixels of adjacent left and right image data.